1. Field of the Invention
This disclosure relates to a vibrator having excitation electrodes in each of upper and lower surfaces of a piezoelectric thin film, an electronic component having the vibrator, and a method of manufacturing the vibrator.
2. Description of Related Art
For example, as a vibrator based on a piezoelectric/inverse piezoelectric effect of a piezoelectric thin film made of aluminum nitride (AlN) and the like, there is known a disk resonator (vibrating body) in which the piezoelectric thin film is formed, for example, in a disk shape, and excitation electrodes made of, for example, molybdenum (Mo) and the like are formed in each of upper and lower surfaces of the piezoelectric thin film. In such a disk resonator, contour vibration is generated along a circumferential direction such that the piezoelectric thin film expands and contracts in a radial direction of the piezoelectric thin film by using a center of the piezoelectric thin film as a nodal point. In this regard, in order to support (fix) the disk resonator, for example, onto a silicon substrate using a simple structure while hindrance of contour vibration is suppressed, there is known a technique in which a pair of disk resonators are arranged side by side in a horizontal direction, the outer circumferences of the disk resonators are connected with a connecting portion, for example, having an approximately box shape, and the lower surface of the connecting portion is fixed to the silicon substrate.
That is, in order to vibrate the disk resonators in phase, the diameter, mass, or the like of the piezoelectric thin film are mutually aligned between the disk resonators. In addition, in order to provide the same electric potential between the upper excitation electrodes and between the lower excitation electrodes, an electric signal is input/output to/from the excitation electrodes through the connecting portion. Therefore, since a nodal point (or node) of the contour vibration is formed in the connecting portion, each disk resonator is supported while hindrance of contour vibration is suppressed. When the resonance frequency is adjusted after such a disk resonator is manufactured, the piezoelectric thin film or the excitation electrode of each of disk resonators is perforated, for example, through laser processing to change (reduce) rigidity or mass of the disk resonator.
Here, in a configuration having a pair of disk resonators connected with a connecting portion, vibration of the disk resonator is hindered by the connecting portion in practice as recognized from the simulation result described below, which is not an ideal vibration mode. For this reason, compared to a case where vibration is generated in an ideal vibration mode, the electric characteristic of the disk resonator is deteriorated. In addition, if a processing position, a processing amount, and the like are deviated between a pair of the disk resonators when the aforementioned laser processing is performed, vibration balance between the disk resonators is lost. Therefore, elastic energy may leak through the connecting portion, and the Q-value may be degraded. Japanese Application No. 2008-124747 discloses a pair of disk resonators connected with a connecting portion. In addition, the contour vibration type resonator is disclosed in Japanese Patent Application No. 2005-159620, Japanese Patent Application No. 2007-535275, Japanese Patent Application No. 2005-348222, and Japanese Patent Application No. 2006-41911. However, the aforementioned patent documents fail to discuss the aforementioned problems.
A need thus exists for a vibrator which is not susceptible to the drawback mentioned above.